In the known processes of microfiltration and ultrafiltration, mainly tube- or plate-shaped membrane filtration modules are used. The liquid to be clarified or filtered flows crosswise to the filtration device over the membrane filtration surface. Thus, the clarified juice, the permeate, is separated from the liquid containing the filtration residues. This procedure is repeated from time to time in one circuit of the retentate. During batch processing the concentration of the filtration residues, the so-called proportion of solids, constantly increases.
The disadvantage of these known processes is that with increasing filtration time and increasing proportion of solids in the retentate, a decrease occurs in the filtration yield, e.g. the amount of permeate outflow per filtration surface unit and time unit. This decrease in the filtration yield can amount to less than half the starting value. For achieving a certain filtration yield, the reduced filtration yield must be taken into account in the design of ultrafiltration and microfiltration units. However, this requires large filtration surfaces and leads to expensive, partially uneconomical units with a large number of filtration modules.